[petsc-users] Profile a matrix-free solver.

[Matthew Knepley]

On Thu, Jan 14, 2016 at 3:01 PM, Song Gao <song.gao2 at mail.mcgill.ca> wrote:

> Hello,
>
> I am profiling a finite element Navier-Stokes solver. It uses the
> Jacobian-free Newton Krylov method and a custom preconditoner LU-SGS (a
> matrix-free version of Symmetic Gauss-Seidel ). The log summary is
> attached. Four events are registered.  compute_rhs is compute rhs (used by
> MatMult_MFFD). SURFINT and VOLINT are parts of compute_rhs. LU-SGS is the
> custom preconditioner. I didn't call PetscLogFlops so these flops are
> zeros.
>
>  I'm wondering, is the percent time of the events reasonable in the table?
> I see 69% time is spent on  matmult_mffd. Is it expected in matrix-free
> method? What might be a good starting point of profiling this solver? Thank
> you in advance.
>

The way I read this, you are taking about 23 iterates/solve, and most of
your work is residual computation which should
be highly parallelizable/vectorizable. This seems great to me.

   Matt


>
>
> Song Gao
>



-- 
What most experimenters take for granted before they begin their
experiments is infinitely more interesting than any results to which their
experiments lead.
-- Norbert Wiener
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